#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;

const int N = 210, INF = 0x3f3f3f3f;//?

int n, m, Q;
int dist[N][N];

void floyd()
{
    for(int k = 1; k <= n; k ++)//一定要在最外层
        for(int i = 1; i <= n; i ++)
            for(int j = 1; j <=n; j ++)
                dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);//i->j 与 i->k->j 哪个小 
}

int main()
{
    cin >> n >> m >> Q;

    memset(dist, 0x3f, sizeof dist);
    for(int i = 1; i <=n ; i ++)    dist[i][i] = 0;//刚开始每个点都可以到达自己所以=0
    while(m --)
    {
        int a, b, w;
        cin >> a >> b >> w;
        dist[a][b] = min(dist[a][b], w);
    }

    floyd();

    while(Q --)
    {
        int a, b;
        cin >> a >> b;
        if(dist[a][b] > INF / 2)    puts("impossible");// 因为会有INF - 2， 所有不一定是INF
        else cout << dist[a][b] << endl;
    }
    return 0;
}